Compensation of THz spectrum spurious oscillations by local apodization

In a THz time-domain spectroscopy (THz-TDS) system, Etalon effects, which appear as secondary peaks in the time-domain signal, produce amplitude spurious oscillations in the spectrum. For preventing this, in the case of multiple reflections inside the detector crystal, an anti-reflection coating can be used. For other cases, like secondary peaks produced by the sample, a compensation algorithm based in convolution and other techniques have been reported in the literature. In this paper, a method based on local apodization is proposed as an alternative to reduce spurious oscillations in THz-TDS spectrums. We show that, using a rectangular apodization function, it is possible to compensate the spurious oscillations with reduced degradation of other spectral features. The proposed method depends on three parameters, which gives it flexibility, though optimal settings need to be found by trial and error at this point. This method can compensate any secondary peak regardless of the source producing it.